Control for synchronized pump motors



Nov. 18, 1947. H. H. CURRY 2,430,917

CONTROL FOR SYNCHRONIZED PUMP MOTORS Filed Jan. 7, 1944 2 Sheets-Sheet 1 INVENTOR HERMAN .H. CURRY ATTORNEY Nov. 18, 1947 H. H. CURRY 7 'CONTROL FOR SYNCHRONIZED PUMP MOTORS Filed Jan. 7, 1944 2 Sheets-Sheet 2 INVENTOR HERMAN H, CURRY BY rww AT TORNE Y Patented Nov. 18, 1947 CONTROL FOR SYNCHRONIZED PUMP MOTORS Herman H. Curry, United States Coast Guard, Morristown, N. J.

Application January 7, 1944, Serial No. 517,297

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 3 Claims.

The present invention relates to a variable capacity pump of the type having shafts adapted to rotate at variable phase angles with each other.

More specifically the invention contemplates driving the shafts of a variable capacity pump of the opposed piston type by means of electric motors electrically connected through means for varying the phase of the currents supplied thereto.

Pumps of the kind here considered are desirable as boiler feed pumps for modern high-pressure marine power plants in which the steam generators are of small water capacity, consequently requiring close control of water fed into the boiler. Variable stroke feed pumps relying upon a mechanical linkage for varying the stroke of piston are complex in structure, cause uneven wear from long operation at one adjustment and are unduly heavy and expensive.

It is the object of this invention to provide a variable capacity pump of the opposed piston type driven at substantially constant speed and piston stroke by electric motors connected electrically by means of phase changing devices.

Another object of the invention is to control the volume of water discharged by the pump by regulating the phase displacement of the shafts and motors by means of automatic control of the phase changing device.

Other objects of the invention will be more fully disclosed in the following specification and claims.

Fig. 1 is a schematic diagram of the pump and means for driving same.

Fig. 2 is a schematic diagram of a modified form of the invention.

Referring to Fig. 1 of the drawing, the pump comprises a cylinder In provided with opposed pistons H and l 2 coupled to the crankarms I 6 and ii of the orankshafts by connecting rods I3 and Hi. The gears I! and i8, fixed to the ends of the crankshafts 8 and 9 mesh with pinions l9 and as. Inlet port 38 and outlet port 23, located centrally of the cylinder I0, are provided with flap valves 2i and 22. When pistons II and I2 are working in opposition, that is moving in opposite directions at the same time, they will cause water to flow through port 22 on the suction stroke and through port 23 on the compression stroke in the direction indicated by the arrows. In practice the pump will consist of three cylinders with pistons driven from the same pair of shafts, but with crank throws spaced 120 apart as is well known in the art. When the pistons I l and I2 move in unison, that is, in the same direction at the same time, their relative displacement is zero and no liquid will flow through the pump. However, when the pistons move in opposite directions at the same time their relative displacement will cause a flow of water through the pump, the quantity depending upon the degree of phase displacement of one shaft with respect to the other.

'As it is obvious that many different arrangements of cylinders are possible, such as side by side, rather than opposed, as illustrated, the invention is not limited to the specific pump shown, but includes pumps similar in function though different in form, design or arrangement.

Rotation of the crankshafts at equal speed with provision for altering the phase angle of one with respect to the other is accomplished by the use of similar electric motors driving pinions l9 and 28 through coupling means 28 and 29. The motors are alternating current induction motors with wound rotors provided with slip rings. These are depicted as three phase machines in Fig. 1 of the drawing. The stators are connected to an alternating current power line through any conventional starting means such as switch 31.

The stators when energized produce rotating fields therein and, as the motors are similar, the fields rotate at the same speed. These fields react with their respective rotors to produce rotation thereof. If the rotor windings of one machine are directly electrically connected to the rotor windings of the other, the two machines will then operate with the same phase relationship, once they are started, in accordance with well known electrical principles. A diiierence in the phase of the voltage in the rotors of the two motors will result in a corresponding difference in the relative angular displacement of the rotors. This small angular shift does not interfere with their operation in synchronism. Thus, by inserting a phase changing means in the circuit connecting the rotors the phase relationship thereof may be varied.

The phase changing device shown in the drawing is an induction regulator, though any other phase changing device may be used. The primary winding 35 of the regulator is connected to the rotor 24 through its slip rings while the secondary winding 3| is similarly connected to the rotor 25 of the other motor. As the phase of the voltage generated in the secondary windings of the regulator varies directly with the electrical space position thereof, movement of the regulator secondary 3| will produce a phase difference between the input and output voltage thereof and cause a corresponding shift in the phase angle of the rotor 25 with respect to rotor 24. This in turn causes a change in th relative angular displacement of the crankshafts and the displacement of the pistons I l and I2 and a consequent change in the pump output.

The coupling between the motor rotors 24 and 25 through the phase changing means, the induction regulator of Fig. 1, may be considered as introducing a counter electromotive force in the leading rotor circuit and an aiding electromotive force in the lagging rotor circuit which will tend to keep the motors synchronized. While the introduction of the resistance and reactance of the phase changing means in the rotor circuit will alter the characteristics of the motors, such alteration is relatively slight due to the fact that the small synchronizing torque required needs a phase changing means of low rating and consequently low impedance. For example, a phase changing device with a rating of 25% of that of either motor would be sufficient to keep the motors synchronized under all conditions of operation of the pump.

The phase difference produced by the induction regulator and, consequently, the phase relation of the motors and crankshafts may be made a function of the demand upon the pump. For example the steam pressure or water level in a boiler fed by the pump, may operate on a suitable pressure responsive means 36 to control the switch 35 in the split field of the series motor 34 driving the secondary 3| of the regulator through worm 33 and gear 32 to alter the phase relation of the means driving the pump so that the output thereof may be increased or decreased depending upon the direction of rotation of the control motor 34.

The pump shown in Fig. 2 consists of a variable capacity pump similar to that previously described in connection with the device shown in Fig. 1. The crankshafts of the pump are driven by means of two synchronous motors 50 and 56 coupled thereto through suitable gearing. These motors operate in phase and at a constant speed. The relative angular displacement of the crankshafts is altered by changing the phase of the power supplied to one of the motors with respect to the other. The phase changing device shown in Fig. 2 is an induction regulator. The primary of the regulator and the synchronous motor 50 are connected to a suitable source of alternating current through any conventional starting means such as switch 54. The regulator secondary 53, connected to motor 5|, supplies power thereto at a phase angle determined by the position of the secondary 53 with respect to the primary 52. Changing the angular position of the secondary 53 changes the phase of the power supplied to motor 5| and consequently the angular displacement of the crankshaft driven thereby is altered with respect to that of the crankshaft driven by motor 56 which operates from power direct from the line.

A pressure response device 55 subject to a condition of the boiler supplied by the pump may control the operation thereof. The device 55 operates a switch 56 in the split field of motor 51 to turn secondary 53 of the induction regulator thru a worm and gear 58 to increase or decrease the phase displacement between the power supplied the motors and consequently vary the output of the pump.

While the drawings show the use of an induction regulator to produce phase differences in the voltages, it is obvious that other means, such as a phase changing transformer, may be substituted therefore.

While I have described the preferred form of my invention I do not wish to limit myself to the precise details as shown but wish to avail myself of such variations and modifications as may come within the scope of the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. A motor control system comprising a plurality of motors, each having a rotor member and a stator member, multiphase windings on each of said members, one of said windings of each motor being adapted for connection to an alternating current supply source, connections between the remaining winding of said motors, and impedance means in said connections for varying the relative phases of the currents passing between the remaining windings of said motors.

2. A motor control system comprising a plurality of motors, each having a rotor member and a stator member, multiphase windings on each of said members, one of said windings of each motor being adapted for connection to an alternating current supply source, an induction regulator having multiphase rotor windings and multiphase stator windings, connections between the induction regulator rotor windings and at least one of the remaining windings of said motors, and connections between the induction regulator stator windings and the other of the remaining windings of the motors.

3. A motor control system comprising a plurality of motors, each having a rotor member and a stator member, three-phase windings on each of said members, one of said windings of each motor being adapted for connection to an alternating current supply source, an induction regulator having three-phase rotor windings and three-phase stator windings, connections between the induction regulator rotor windings and at least one of the remaining windings of said motors, and connections between the induction regulator stator windings and the other of the remaining windings of the motors.

HERMAN H. CURRY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 886,047 Flinn Apr. 28, 1908 1,441,310 Thomas Jan. 9, 1923 1,471,901 Lemp Oct. 23, 1923 1,572,365 Rotter Feb. 9, 1926 1,965,288 Hillier July 3, 1934 1,965,414 Hardy July 3, 1934 1,983,229 Hillier et al. Dec. 4, 1934 1,998,939 Mittag Apr. 23, 1935 2,160,687 Stubbs May 30, 1939 2,172,103 Kotaki Sept. 5, 1939 OTHER REFERENCES Standard Handbook for Electrical Engineers, 7th ed., page 737, sec. 7, par 280. 

